Method for forming large-size curved thin-walled metal skin

ABSTRACT

A method for forming a large-size curved thin-walled metal skin is disclosed, wherein the position and size characteristics of stiffeners on a curved panel is extracted; the thickness of the curved panel and the thin-walled skin after assembly is assumed to be m, and a forming surface of the punch is offset outwards along a normal line by the thickness m to obtain the characteristics of the inner surface of a female die; the number of the discrete support moulds is set to be the same as the number n of the stiffeners based on the size and distribution of the stiffeners on the curved panel; and the punch and the female die combined with the discrete support moulds are used to carry out stamping of a curved thin-walled slab to obtain a required thin-walled skin component.

TECHNICAL FIELD

The present invention relates to a method for forming a metal skin, inparticular to a method for forming a large-size curved thin-walled skin.

BACKGROUND

In the fields of aerospace and weapon equipment, achieving a lightweightstructure is one of the main goals pursued. In order to reduce theweight of the structure, it is necessary to optimize the design ofcomponents on the premise of meeting the requirements of use. Forexample, many lightweight hollow composite structures are used on arocket or a missile, such as panels of a rocket propellant tank andfairings of a missile. This kind of lightweight structure usuallyconsists of a curved panel and a thin-walled skin matched therewith. Thecurved panel is generally composed of thin-walled webs and stiffenersconnected thereto, and the stiffeners are used to improve the overallstiffness of the panel. In order to further improve the stiffness of thecurved panel and realize the continuity of the surface on the side withthe stiffeners, it is necessary to provide the thin-walled skin matchedtherewith outside the discretely distributed stiffeners.

The above-mentioned lightweight hollow composite structures usually haverelatively large sizes, and the lengthwise sizes can reach severalmeters or even dozens of meters. In order to further reduce weight,lightweight and high-strength aluminum alloy materials, such as 2024 and2219, are mostly used as materials for the curved panel and thethin-walled skin, wherein the curved panel is usually made of a thickaluminum alloy plate with a wall thickness of 20-50 mm, and thethin-walled skin is usually made of a thin aluminum alloy plate with awall thickness of 2-5 mm. As the thickness of the thick aluminum alloyplate used to manufacture the panel is very different from that of thethin aluminum alloy plate used to manufacture the skin, differentforming methods and separate mould tooling are required.

At present, the forming methods of the curved panel include pressbending, cold roll, stamping, etc. For a single-curvature cylindrical orconical panel, forming can be realized by the method of press bending orcold roll. However, for a curved panel with a small bending radius or ahigh dimensional accuracy requirement, dimensional accuracy requirementcannot be met often by press bending or cold roll. In this case,stamping need to be carried out by a rigidity punch and a rigidityfemale die. The rigidity punch and the rigidity female die need to bespecially designed and manufactured according to the shape and size of aspecific panel component.

For a thin-walled skin, forming is often realized by the methods such asstretching and stamping. During the stretch-forming of a large-sizethin-walled skin, the edge of a rectangular metal blank need to beclamped with jaws, and then the middle area of the metal blank isdeformed under the action of a stretching die to obtain a requiredprofile shape. After the stretch-forming, only part of the middle areaof the metal blank is fitted with the stretching die, and othersurrounding material will be removed as a process remnant Therefore, themethod of stretching is difficult to be used for forming a thin-walledskin with an obvious curved surface and especially with a doublecurvature. In this case, it is necessary to use mutually matchedrigidity punch and rigidity female die to obtain a required thin-walledskin through stamping.

Since punches, female dies and corresponding tooling in one-to-onecorrespondence with parts to be formed are generally required to beprocessed for stamping, the cost of moulds and tooling is relativelyhigh, and this is especially true for large-sized components. Forexample, for a curved panel and a thin-walled skin with a length ofabout 3 m and a width of 1 m, the cost of moulds and tooling used forstamping can reach hundreds of thousands yuan or even millions yuan. Atthe same time, large-scale special equipment is required for themanufacturing of large-size moulds and tooling, and it will take severalweeks or an even longer time to complete the manufacturing. Therefore,it is very important to reduce the cost of moulds and tooling whileensuring the smooth forming of components and obtaining a high formingaccuracy when the method of stamping must be used.

In order to solve the problems of high component manufacturing cost,long production cycle, high requirements for mould and toolingmanufacturing equipment, and high requirements for the use of theequipment due to the need of separately manufacturing large-sized mouldsand tooling when the existing method of stamping is used to manufacturea large-size curved panel and a thin-walled skin, it is necessary todevelop a new method for forming a large-size curved thin-walled skin.

SUMMARY

In order to solve the problems of high component manufacturing cost,long production cycle, high requirements for mould and toolingmanufacturing equipment, and high requirements for the use of theequipment due to the need of separately manufacturing large-sized mouldsand tooling when the existing method of stamping is used to manufacturea large-size curved panel and a thin-walled skin, the present inventionproposes a method for forming a large-size curved thin-walled metalskin.

The technical solution of the present invention is:

A method for forming a large-size curved thin-walled metal skin,comprising the following steps:

Step 1: extracting the position and size characteristics of stiffenerson a curved panel according to the assembly relationship between thecurved panel and a thin-walled skin;

Step 2: assuming that the thickness of the curved panel and thethin-walled skin after assembly is m, determining the size of a formingpunch based on the shape and size of the curved panel, and offsetting aforming surface of the punch outwards along a normal line by thethickness m based on the size of the forming surface to obtain thecharacteristics of the inner surface of a female die;

Step 3: determining the size of discrete support moulds to be the sameas that of the curved panel according to the thickness of the curvedpanel, and determining forming surfaces of the discrete support mouldsbased on the inner surface of the forming thin-walled skin;

Step 4: setting the number of the discrete support moulds to be the sameas the number n of the stiffeners based on the size and distribution ofthe stiffeners on the curved panel, and the positions of the discretesupport moulds on the punch are consistent with the positions of thestiffeners on the curved panel;

Step 5: processing and manufacturing the punch, the female die and ndiscrete support moulds according to step 2 and step 3;

Step 6: fixing the n discrete support moulds on the punch according tostep 4, and the relevant positions for connecting the discrete supportmoulds are corresponding to the positions of the stiffeners on thecurved panel during assembly; and

Step 7: using the punch and the female die combined with the discretesupport moulds to carry out stamping of a curved thin-walled slab toobtain a required thin-walled skin component.

The present invention has the following beneficial effects:

(1) In the method for forming a large-size curved thin-walled metal skinof the present invention, the n discrete support moulds used arecombined with the curved panel forming punch, then the stamping of thethin-walled skin is carried out, and the positions of the discretesupport moulds are consistent with the positions of the stiffeners onthe curved panel, so that it can be ensured that the part of thethin-walled skin corresponding to the stiffeners obtains sufficientlyhigh shape and dimensional accuracy, thereby realizing the subsequentreliable connection of the thin-walled skin and the panel.

(2) In the method for forming a large-size curved thin-walled metal skinof the present invention, the n discrete support moulds used are only inpartial contact with the thin-walled slab, so that the areas on thethin-walled skin that do not need to be assembled with the stiffenersare in a relatively free state during stamping, which can avoidunreasonable, uncontrollable or redundant deformation in such areas whena solid punch is used for stamping.

(3) In the method for forming a large-size curved thin-walled metal skinof the present invention, the connecting positions of the discretesupport moulds used on the punch can be easily adjusted, so that theproblems such as wrinkling and warping which may occur during a formingprocess can be easily eliminated.

(4) In the method for forming a large-size curved thin-walled metal skinof the present invention, the discrete support moulds used can beassembled and connected with the punch, so that the discrete supportmoulds are easy to replace, and can be replaced by different discretesupport moulds to be used for forming thin-walled skins of differentthicknesses.

(5) In the method for forming a large-size curved thin-walled metal skinof the present invention, the discrete support moulds used only need tobe in contact with the thin-walled slab in partial areas, so that theshape thereof is simple, the manufacturing cycle is short, and themanufacturing cost is greatly reduced.

DESCRIPTION OF DRAWINGS

FIG. 1(a) is a schematic diagram of a curved panel.

FIG. 1(b) is a schematic diagram of a thin-walled skin.

FIG. 2 is a schematic diagram of stamping of a curved panel.

FIG. 3 is a schematic diagram of forming a large-size curved thin-walledskin by a discrete support mould;

FIG. 4 is a schematic diagram of assembly of a discrete support mouldand a curved panel forming punch;

FIG. 5 is a schematic diagram of action of a discrete support mould on athin-walled skin.

In the figures: 1 curved panel; 2 thin-walled skin; 3 punch; 4 femaledie; 5 connecting bolt; 6 discrete support mould.

DETAILED DESCRIPTION

The technical solution of the present invention is further describedbelow in combination with the drawings and specific embodiments.

Embodiment 1

Referring to FIG. 3 for description, a method for forming a large-sizecurved thin-walled metal skin, comprising the following steps:

Step 1: extracting the position and size characteristics of stiffenerson a curved panel according to the assembly relationship between thecurved panel and a thin-walled skin;

Step 2: assuming that the thickness of the curved panel and thethin-walled skin after assembly is m, determining the size of a formingpunch based on the shape and size of the curved panel, and offsetting aforming surface of the punch outwards along a normal line by thethickness m based on the size of the forming surface to obtain thecharacteristics of the inner surface of a female die;

Step 3: determining the size of discrete support moulds to be the sameas that of the curved panel according to the thickness of the curvedpanel, and determining forming surfaces of the discrete support mouldsbased on the inner surface of the forming thin-walled skin;

Step 4: setting the number of the discrete support moulds to be the sameas the number n of the stiffeners based on the size and distribution ofthe stiffeners on the curved panel, and the positions of the discretesupport moulds on the punch are consistent with the positions of thestiffeners on the curved panel;

Step 5: processing and manufacturing the punch, the female die and ndiscrete support moulds according to step 2 and step 3;

Step 6: fixing the n discrete support moulds on the punch according tostep 4, and the relevant positions for connecting the discrete supportmoulds are corresponding to the positions of the stiffeners on thecurved panel during assembly; and

Step 7: using the punch and the female die combined with the discretesupport moulds to carry out stamping of a curved thin-walled slab toobtain a required thin-walled skin component.

The n discrete support moulds used are combined with the curved panelforming punch, then the stamping of the thin-walled skin is carried out,and the positions of the discrete support moulds are consistent with thepositions of the stiffeners on the curved panel, so that it can beensured that the part of the thin-walled skin corresponding to thestiffeners obtains sufficiently high shape and dimensional accuracy,thereby realizing the subsequent reliable connection of the thin-walledskin and the curved panel.

Embodiment 2

Referring to FIG. 4 for description, a method for forming a large-sizecurved thin-walled metal skin, comprising the following steps:

In step 6, the n discrete support moulds are dispersedly arranged on thepunch, the dispersing positions of discrete support moulds can bedetermined according to the positions of the stiffeners on the curvedpanel, the replacement stiffeners of the discrete support moulds aredistributed on the punch, and the dispersing positions of the discretesupport moulds can also be adjusted according to the forming conditionof the thin-walled slab after forming. Other steps are the same as thosein embodiment 1.

When a sheet is formed by a solid die, due to the uneven loaddistribution and different contact states on various parts of a slab,the problems of wrinkling and warping are prone to occur during forming;whereas a certain distance exists among the discrete support moulds, sothat the problems such as wrinkling and warping which may occur during aforming process can be easily eliminated by adjusting the positions ofthe discrete support moulds on the punch. The discrete support mouldsare assembled and connected with the punch, so that the discrete supportmoulds are easy to replace, and can be replaced by different discretesupport moulds to be used for forming thin-walled skins of differentthicknesses, which saves the material and processing cost of the moulds.

Embodiment 3

Referring to FIG. 5 for description, a method for forming a large-sizecurved thin-walled metal skin, comprising the following steps:

In step 6, the discrete support moulds and the punch can be effectivelyconnected by bolts, and each discrete support mould is composed of aplurality of small moulds with surface shape and size requirements. Eachdiscrete support mould used in other steps is composed of a plurality ofsmall mould blocks, and a gap exists among adjacent small mould blocks.Other steps are the same as those in embodiment 1.

In a traditional stamping process, most of the moulds are in a solidform, which are prone to have excessive local contact stress andredundant deformation. The discrete support moulds composed of aplurality of small mould blocks are only in partial contact with thethin-walled slab, so that the areas on the thin-walled skin that do notneed to be assembled with the stiffeners are all in a relatively freestate, which can avoid unreasonable, uncontrollable or redundantdeformation in such areas when a solid punch is used for forming.

1. A method for forming a large-size curved thin-walled metal skin,comprising the following steps: step 1: extracting the position and sizecharacteristics of stiffeners on a curved panel according to theassembly relationship between the curved panel and a thin-walled skin;step 2: assuming that the thickness of the curved panel and thethin-walled skin after assembly is m, determining the size of a formingpunch based on the shape and size of the curved panel, and offsetting aforming surface of the punch outwards along a normal line by thethickness m based on the size of the forming surface to obtain thecharacteristics of the inner surface of a female die; step 3:determining the size of discrete support moulds to be the same as thatof the curved panel according to the thickness of the curved panel, anddetermining forming surfaces of the discrete support moulds based on theinner surface of the forming thin-walled skin; step 4: setting thenumber of the discrete support moulds to be the same as the number n ofthe stiffeners based on the size and distribution of the stiffeners onthe curved panel, and the positions of the discrete support moulds onthe punch are consistent with the positions of the stiffeners on thecurved panel; step 5: processing and manufacturing the punch, the femaledie and n discrete support moulds according to step 2 and step 3; step6: fixing the n discrete support moulds on the punch according to step4, and the relevant positions for connecting the discrete support mouldsare corresponding to the positions of the stiffeners on the curved panelduring assembly; and step 7: using the punch and the female die combinedwith the discrete support moulds to carry out stamping of a curvedthin-walled slab to obtain a required thin-walled skin component.